1. Field of the Invention
The present invention generally relates to improvements in an extrusion die used when pelletizing plastics and more specifically relates to a removable center or die plate insert for an extrusion die enabling the portion of the extrusion die having the orifices therein to be easily removed for cleaning or removed for replacement with a die plate insert having a different number of orifices or different size of orifices thereby substantially reducing the down time of an underwater plastic pelletizing machine especially in installations where product changes are frequent.
2. Information Disclosure Statement
Plastics are frequently pelletized by extruding plastic through extrusion dies having a plurality of orifices therein with the downstream end of the orifices having a wear surface engaged by a rotating blade assembly which cuts the extruded plastic into pellets. In certain production techniques such as in relatively small compounding operations, product changes are rather frequent. In making product changes, it frequently is necessary to replace the extrusion die with a die having a different size or number of extrusion orifices. Also, it is necessary to remove the extrusion die plate for cleaning purposes from time to time.
The general structure of an underwater pelletizer of the above described type is disclosed in U.S. Pat. No. 4,123,207, issued Oct. 31, 1978, for UNDERWATER PELLETIZER AND HEAT EXCHANGER DIE PLATE. Additionally, the following U.S. patents relate to extrusion die structures:
U.S. Pat. No. 3.905,743 Sept. 10, 1975
U.S. Pat. No. 3,947,214 Mar. 30, 1976
U.S. Pat. No. 4,182,603 Jan. 8, 1980
U.S. Pat. No. 4,290,989 Sept. 22, 1981
U.S. Pat. No. 4,343,609 Aug. 10, 1982
When removing electrically heated extrusions dies, the cartridge heaters used to heat the die plate must be extracted or removed thus resulting in maintenance problems since the heating cartridges frequently become stuck in the cartridge cavity in the die plate and their lead wires sometimes become frayed. In addition, the loss of time required to remove the cartridges, the die plate, install another die plate and reassemble the heating cartridges is substantial and the cost of clean-up and maintenance has become a major factor in the economics of pelletizing plastics. None of the prior art plastic pelletizers provide an effective solution to this ongoing problem and cost.